Field of the Invention
The present invention relates to a circuit for a focused ion beam (FIB) sensor which can be used, in particular, for the protection of chip card and smart card ICs.
Electronic circuits, and primarily circuits provided with a memory for holding personal information, must must be protected against unauthorized analysis, in particular against covert discovery of the stored data. One possible attack can be effected by FIB (Focused Ion Beam). Such an attack can be detected by a circuit suitable for this, so that suitable countermeasures can be initiated in the case of an attack that has been ascertained. By way of example, it can be ensured that during or after such an attack, the electronic circuit is rendered unusable to the extent that information can no longer be read out in an unauthorized manner.
A protection circuit suitable for this constitutes a so-called “FIB sensor” which detects electrical charging—effected by the attack—of the protection circuit or of a circuit section provided for this. The charge detected by the FIB sensor as a result of the FIB attack leads to a detectable alteration of the charge content, in order to make it recognizable that the circuit was the target of an FIB attack. The FIB sensor therefore comprises a memory cell with a driver circuit and an antenna—connected to the memory cell—as electrical conductor, on which electrical charges are accumulated during an FIB attack.
The charge is fed to the memory cell in such a way that the memory cell experiences a detectable alteration of its charge content. A further circuit section is provided as driver circuit for ascertaining the state of the memory cell of the FIB sensor. It must thereby be ensured that this circuit section is connected or can be connected in such a way that the charge collected by the antenna in the case of a FIB attack does not flow away through the driver circuit before the reprogramming of the memory cell takes place.
European published patent application EP 0 510 434 A2 describes a circuit configuration for preventing an analysis of a circuit, in which a PIN photodiode is provided for the detection of impinging radiation and is connected between the inverting and the non-inverting inputs of an operational amplifier. The output of the opamp controls a switch which disconnects a volatile RAM memory to be protected from the voltage supply in the event of irradiation.